Linux下的C语言编程——waitpid函数的应用

小灰灰 2022-07-14 04:14 257阅读 0赞

头文件

\#include <sys/type.h>

\#include <sys/wait.h>

定义函数pid\_t waitpid(pid\_t pid, int \* status,int options)

waitpid()会暂时停止目前进程的执行，知道有信号来到或子进程结束。若果在调用wait（）时子进程已经结束，则wait（）会立即返回子进程结束状态值。

子进程的结束状态值会有参数status返回，而子进程也会一块返回。

#include <stdio.h>
    #include <stdlib.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <sys/wait.h>
    
    void die(const char *msg)
    {
            perror(msg);
            exit(1);
    }
    
    void child2_do()
    {
            printf("In child2: execute 'date'\n");
    
            sleep(5);
            if (execlp("date", "date", NULL) < 0) {
                    perror("child2 execlp");
            }
    }
    
    void child1_do(pid_t child2, char *argv)
    {
            pid_t pw;
    
            do {
                    if (*argv == '1') {
                            pw = waitpid(child2, NULL, 0);
                    }
                    else {
                            pw = waitpid(child2, NULL, WNOHANG);
                    }
                    if (pw == 0) {
                            printf("In child1 process:\nThe child2 process has not exited!\n");
                            sleep(1);
                    }
            }while (pw == 0);
    
            if (pw == child2) {
                    printf("Get child2 %d.\n", pw);
                    sleep(5);
                    if (execlp("pwd", "pwd", NULL) < 0) {
                            perror("child1 execlp");
                    }
            }
            else {
                    printf("error occured!\n");
            }
    }
    
    void father_do(pid_t child1, char *argv)
    {
            pid_t pw;
    
            do {
                    if (*argv == '1') {
                            pw = waitpid(child1, NULL, 0);
                    }
                    else {
                            pw = waitpid(child1, NULL, WNOHANG);
                    }
    
                    if (pw == 0) {
                            printf("In father process:\nThe child1 process has not exited.\n");
                            sleep(1);
                    }
            }while (pw == 0);
    
            if (pw == child1) {
                    printf("Get child1 %d.\n", pw);
                    if (execlp("ls", "ls", "-l", NULL) < 0) {
                            perror("father execlp");
                    }
            }
            else {
                    printf("error occured!\n");
            }
    }
    
    int main(int argc, char *argv[])
    {
            pid_t child1, child2;
    
            if (argc < 3) {
                    printf("Usage: waitpid [0 1] [0 1]\n");
                    exit(1);
            }
    
            child1 = fork();
    
            if (child1 < 0) {
                    die("child1 fork");
            }
            else if (child1 == 0) {
                    child2 = fork();
    
                    if (child2 < 0) {
                            die("child2 fork");
                    }
                    else if (child2 == 0) {
                            child2_do();
                    }
                    else {
                            child1_do(child2, argv[1]);
                    }
            }
            else {
                    father_do(child1, argv[2]);
            }
    
            return 0;
    }